<!DOCTYPE html>
<html>

<head>
    <meta charset="UTF-8">
    <meta content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=0;" name="viewport" />
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>canvas 圆形进度条效果</title>
    <style>
        * {
            margin: 0;
            padding: 0;
        }

        body {
            text-align: center;
            background-color: #000;
        }
    </style>
</head>

<body>
    <canvas id="canvas" width="500" height="500" style="background:#000;"></canvas>
    <script>
        window.onload = function () {
            var canvas = document.getElementById('canvas'),  //获取canvas元素
                context = canvas.getContext('2d'),  //获取画图环境，指明为2d
                centerX = canvas.width / 2,   //Canvas中心点x轴坐标
                centerY = canvas.height / 2,  //Canvas中心点y轴坐标
                rad = Math.PI * 2 / 100, //将360度分成100份，那么每一份就是rad度
                speed = 0.1; //加载的快慢就靠它了 
            //绘制蓝色外圈
            function blueCircle(n) {
                context.save();
                context.strokeStyle = "#fff"; //设置描边样式
                context.lineWidth = 5; //设置线宽
                context.beginPath(); //路径开始
                context.arc(centerX, centerY, 100, -Math.PI / 2, -Math.PI / 2 + n * rad, false); //用于绘制圆弧context.arc(x坐标，y坐标，半径，起始角度，终止角度，顺时针/逆时针)
                context.stroke(); //绘制
                context.closePath(); //路径结束
                context.restore();
            }
            //绘制白色外圈
            function whiteCircle() {
                context.save();
                context.beginPath();
                context.strokeStyle = "white";
                context.arc(centerX, centerY, 100, 0, Math.PI * 2, false);
                context.stroke();
                context.closePath();
                context.restore();
            }
            //百分比文字绘制
            function text(n) {
                context.save(); //save和restore可以保证样式属性只运用于该段canvas元素
                context.strokeStyle = "#fff"; //设置描边样式
                context.font = "40px Arial"; //设置字体大小和字体
                //绘制字体，并且指定位置
                context.strokeText(n.toFixed(0) + "%", centerX - 25, centerY + 10);
                context.stroke(); //执行绘制
                context.restore();
            }
            //动画循环
            (function drawFrame() {
                window.requestAnimationFrame(drawFrame, canvas);
                context.clearRect(0, 0, canvas.width, canvas.height);
                whiteCircle();
                text(speed);
                blueCircle(speed);
                if (speed > 100) speed = 0;
                speed += 0.1;
            }());
        }
    </script>
</body>

</html>